Many industrial machines and tools are known to be dangerous devices unless used in a certain manner specific to the particular machine or tool and task. For example, the brightness of a welding torch may burn the eyes of an operator unless a protective visor is worn, a chainsaw is more likely to cause a kickback injury if not held correctly, and so on. Situations that can create a safety hazard with a single tool can be quite varied. The welding torch, for example, can burn skin with heat or burn eyes with brightness. The procedures or environments necessary to safely use some dangerous dices can be complicated, with long procedural or operational checklists.
Three example dangerous tools are a welding torch, a forklift, and a chainsaw. A common safety protocol for a welding torch includes requiring an operator to wear safety gear or clothing, such as wearing a flameproof glove on the hand not holding the torch, and wearing a mask to protect the operator's eyes from the brightness of the welding point and to protect the rest of the operator's head from flying sparks or other debris. A simple safety protocol for a forklift includes never attempting to pick up an object weighting more than the maximum load for which the forklift is rated. A safety protocol for a chainsaw includes holding the chainsaw correctly with two hands.
Some safety devices can be integrated into a dangerous tool to require conformity with a safety precaution, but there are limits to what can be integrated into the physical tool itself. A typical chainsaw provides an example of both integrated and hard-to-integrate safety precautions, where an appropriate safety precaution involves both operator hands correctly holding both handholds before allowing the chain to rotate. A commonly integrated precaution is built into the throttle of many chainsaws. The throttle is usually a finger trigger located under the rear handhold, and the trigger cannot be engaged unless a lockout switch on the top of the rear handhold is also depressed. Such a configuration generally prevents any chain motion without one of the operator's hands correctly holding the rear handle.